Tape cartridges in use today incorporate a magnetic tape having data tracks for recording a succession of units of information known as data sets. Each data set consists of a data region within which data is recorded and a data set information table that describes the content of the data region. Data to be recorded is sent to the cartridge by a tape drive and is recorded within the data regions. The data set information table for each data set has a multiplicity of fields each of which has a pre-allocated number of bytes of storage. The fields store records of information such as the data set number, the valid data length, the data set type, and the drive manufacturer identity.
Data written to the tape may be protected from being overwritten. Such data is protected by drive level processing that renders the tape as write-once-read-many (WORM) protected. When trying to protect data written to tape in a WORM environment, safeguards are implemented to prevent the data from being overwritten, accidentally or intentionally.
An inherent feature of WORM data is that, once written, it is protected from being overwritten. Whilst this is desirable for reasons of data integrity and protection, it has the drawback that the media on which the data is recorded may not be re-used when the retention period of the data has expired. One solution has been to destroy the cartridge. This is costly for the user and is also not environmentally friendly.
Another solution has been proposed in which a time stamp is recorded when the data is written. The time stamp is received from a host controlling the tape drive or is generated by the tape drive itself and is used to determine a retention period of the recorded data. Overwriting or erasure of the data is controlled by reference to the time stamp. A difficulty with this solution is that this information must be carefully managed to make robust and secure decisions to allow the erasure of WORM data recorded in the cartridge. Furthermore, recorded time stamps do not allow for flexibility in cases where the retention period has to be changed, for example in relation to data that has to be retained for an enquiry into an insurance claim or a financial investigation.